Electric transmission gearing



NOV. 26, 1940. HEFEL 2,223,210

' ELECTRIC TRANSMISSION GEARING Filed Jan. 20, 1956 2 Sheets-Sheet 1 33 19 o 8 9 26 ii 6' 1 nk 6 4 J Karl Hefel lN ENTcK NOV. 26, 1940. K HEFEL 2,223,210

ELECTRIC TRANSMISS ION GEARING Filed Jan. 20, 1936 2 SheetsSheet 2 (OW K 1L2 AYTTY Patented Nov. 26, 1940 UNITED STATES PATENT OFFICE Application January-20, 1936, Serial No. 59,871 In Austria January 23, 1935 4 Claims.

This invention relates to electric transmission gearing comprising two direct current machines with separate excitation, of which the first acts mainly as generator while the second acts mainly as a motor.

It is the main object of the invention to provide transmission gearing of this nature which. while being of constant high emciency, enables the transmission ratio to be varied within very wide limits, which is of light weight and small dimensions so that it very well suited for use in automobiles and other power-driven vehicles, and in which, finally, alteration of the transmit sion ratio is effected automatically on. the mere operation of the means'i'or controlling the driving motor, for example the engine of an automobile dependence on the speed conditions and resistance to travel at any one time. Further features of the invention relate to means for starting and braking, and also for starting up the driving motor.

In accordance with the invention the one part (armature or field magnet system) of the one machine is coupled to the driving shaft and the other part to the driven shaft, while the one part (armature or field magnet system) of the second machine is coupled to the driven shaft and the other part is stationary; further, the armature windings of both machines are directly connected together to form a closed current circuit, and for varying the transmission ratio there are provided exclusively means for altering the field excitation of the second machine.

A form of construction embodying the invention is shown, by way of example, in the accompanying drawings, in which: V

Fig. 1 is an axial section taken through the transmission gearing in accordance with the invention. v

Fig. 2 is a diagram of connections.

Fig. 3 shows a detail in perspective.

Fig. 4 is a simplified diagram of connections of the gearing in the normal condition, and

Fig. 5 is a similar diagram'of connections of the gearing when used to start up the driving engine with current from a battery.

Referring to the drawings, I denotes the driving shaft, 2 the driven shaft, 3 the armature of the generator part, 4 the commutator of the latter, and 5 the common magnet yoke on which there are mounted the field winding of the generator part 6 and the field winding of the motor part I. 8 denotes the armature of the motor part and 9 its commutator. ID are the brushes of the generator part and H those of the motor The exciting current is fed to the field,

part. winding ofthe motor part through the slip rings 53, while the field winding of the generator part is fed through the slip ring it. The return flow of the current takes place in this case, for instance, through ground. i l denotes the stationary casing of the motor part, while the casing part it rotates with the driven shaft 2.

armature windings or the two machines are directly connected together in circuit, without the interposition of resistances. The feeding of the field windings is effected through the accumulator 30, oi which one pole is grounded at 35, through regulating means to he described in due course, and through the current leads 32 and 33 leading, respectiveiy, to the slip rings i2 it to which the field windings are connected. arrangement of. the radially inwardly or outwardly protecting poles of the magnet systems t, of the motor part and of thegenerator part on the common magnet yoke 5 (there can of course also be provided exciter windings laid in slots instead ofpoles proper) gives the advantage that the brushes l0 and Ii both of the.

generator part and also of the motor part must revolve together with the yoke 5, with the result that the connecting leads from the generator part to the motor part can be stationary, and laid for instance along the brush holders. If an additlon there be employed an equal number of poles for the generator and for the motor the yoke can also be made of light construction, since in this case, given suitable arrangement of the parts, the fluxes of the lines of force of the motor and generator parts partly cancel each other out in the common yoke. It is only when the excitation of the motor part becomes negative, (which case is discussed in detail below), that the two fluxes are additive. Since, however, quite a slight negative flux in' the motor part produces a great increase in the transmission ratio mm: of the gearing, it is perfectly suflicient if the common magnet yoke be designed for 1 to 1 /2 times, and preferably for 1 to 2 times, the magnetic flux of the generator part at full excitation.

The theory of the electric transmission gearing according to the present invention may be explained broadly as follows:

If C, C1, C2, and Ca be taken to be constants (which are determined by the design) then the power (L) transmitted by the gearing may be expressed by the following equation:

L=C1 n2XM2 m being thespeed of. rotational.- the driven shaft in the armature windings by J, then the above it being pre-supposed that the direction of cm is such that the resulting torque exerted bythe motor part upon the common yoke acts in the same direction as the moment of rotation exerted by the generator part upon the common yoke. If m be of reversed polarity, so that the moments of rotation of-the motor part and of. the generator part upon the common yoke counteract ,each other, then om is designated as negative.

On the other hand the power (L1) supplied by the driving engine can be represented by the following equation: Ll=nl a JXC1X0a. 5 Disregarding for'the time being the losses in the gearing, L is equal to L1, and (provided 410 'be maintained constant) there is obtained the relation It follows from this relation that the trans mission ratio m/m becomes reduced the'greater m is. When em equals 0 the ratio mml becomes unity.

If the energy supplied by the-driving machine and the speed 111 be kept constant, a certain 4 maximum speed 11': can be obtained for a given load acting on the shaft 2. To this end, however, the transmission ratio must'be correctly ad"- justed by alteration of the excitation of the motor. This can be done automatically, .as shown in the drawings representing a form of construction of the transmission gearing according to the irivention for use as a gear-box in automobiles.

I6 denotes for example a potentiometer resistance the centre of which is grounded at II, and the two ends of which are connected to the non-grounded. pole of the source of current, in

the present instance of the accumulator 30. A control rod i1 is coupled by means of links 20 and v 2| to the throttle lever in urine automobile encured. At the same time means shouldbe provided to prevent the pair of contacts of the con= trol rod I! from becoming displaced beyond the ends of the resistance I. This can be done for instance by means of sto'ps'provided at the left.

I and right hand ends of the resistance It. The spring 21 in the control rods serves to enable the regulating member", for the driving motor to be nevertheless displaced still further.

The mode of operation ofthis regulating -arrangement will now be explained with reference to Fig. 2 of the drawings. In this figure the con- 'trol rod, n and the sleeve u are shownin-the' l 9 further.

positions they occupy when the vehicle is beinl started'up from a standstill, thev accelerator 0: gas pedal 1 9 being depressed slightlyfrom its no load position so that the internal-combustion engine receives a quantity'of mixture appropriat to the conditions of starting up from a standstill the pedal l9 being also coupled to the regulatin 'rod 28 leading to the throttle of the carburetor Since the brushing contacts 34 areprevented b:

abutrnents from traveling towards the right be the same as when the lowestspeedis engage;

in the case of wheel transmission gearing.

,The Cardan shaft-2 now commences to rotate The driver retains the. setting of the pedal I! fol the time being unaltered. As the speed m increases the sleeve 35 first moves-towards thl right, with the result that the resistance I! ll also correspondingly shifted towards the right The brushing contacts 34 only P ticipate in thi movement of the resistance up to a certain speed nz, until the spring Ills de-tensioned, after whicl they remainmotionlessas long as'the driver doe:

not alter the setting of the pedal ll.

If the outputof the driving engine is the: still greaterthan. the propelling .power at thii speed of the Cardan shaft the vehicle will .be stil further accelerated, that isto say the speed 1::

is still further increased, and consequently through the intermediary of the centrifugal governor It, the sleeve 35, and with it the resistance ii, is still further displaced towards the right while the brushing contacts 34 remain unaffected. These contacts consequently pick up a'lowel voltage .a the potentiometer resistance Ii, witt the res that the excitation of the motor pari is reduced. This however implies an alteration oi the transmission ratio 1mm in the sense of increasing this ratio. The displacement of the resistance l8 comes to an. end when equilibrium becomes established between the output of tht driving engine (with the setting of the pedal I! still unaltered), and the prope power, which corresponds to the terminal s nz.

If the driver now desires to still further in'- crease the speed 'of travel he depresses the pedal In doing so he-o'n the one hand by operation of the regulating rod II, gives the engine more gas with the result that its outpui is increased, and on the other hand, through the intermediary of the control rods 2|, 2|, and i1,

displaces the position of the brushing contact: it towards the right, while the potentiometer resistance remains unaltered as to its position since the velocity of the vehicle'can not have become suddenb' altered. By displacement of the brushing contacts {4. towards the right there is brought about an increase in the excitation of the motor part 1,1 which in its turn implies a decrease in the transmission ratio than. Since the speed a: can not suddenly changethe speed 111 increases increased charging of the driving engine by the operation of the throttle control rod 28, together with the positively increased speed 'm of this engine result in greater driving output which accelerates the vehicle. The speed m is thus increased, the sleeve ,3 is shiftedfurther towards the right. and with it.the resistance II, he that the excitation of the motor part is weakened again, until equilibrium is again established between propelling power and engine output.

According to the above, the tron ratio mzni at any one time is conditioned by the relative position of the resistance it and pair of contacts 24, the position of the resistance being dependent on the speed 11:, and the position of the contacts on the setting of the pedal l9 and therefore on the degree of charging of the driving engine. By suitable construction on the one hand of the control rods ll, 22, 22, 22, 2|, i1, and on the other hand if desired of the arrangement of rods for displacing the resistance II in dependence on the centrifugal governor it, it is possible to ensure that the position of the brushing contacts 24 relatively to the resistance It shall always become so adjusted, in the condition of equilibrium, that certain conditions automatically fulfilled.

An alteration in the shape 'of the guide curv 22 results for example in alteration of the degree 'of charging of the driving engine and its speed of rotation without alteration of the propelling power and velocity of travel, so that this engine has the same output but a different degree of efilciency. Thus, for example,- by suitable shaping of the guide curve 22, it becomes possible at will to ensure the fulfillment of certain pre-conditions as regards eiflciency, rate of acceleration, and the like. 7

The conditions at starting the vehicle from a standstill are as follows: As already pointed out, the generator ileid is normally always excited up to the maximum limit. when the vehicle is standing still, i. e. when the speed 111:0, the mo? tor part of the gearing does not yet generate any counter electromotive force. On the other. hand the driving engine has a speed m as a result of which, when the generator excitation is started, there is set up in the generator part an electromotive force which is counteracted only by the ohmic resistance of the armature windings. The current thus increases disproportionately, so that the resulting Joule eii'ect would be greater than the driving output of the gasoline engine. This would result in stopping the engine and preventing starting of the vehicle. "If however the genof rotation of the shaft I when the erator excitation be weakened, for the purpose of starting. the current in the armature windings does not increase to such a pitch, and the'resulting Joule eii'ect remains less than the output of the driving engine, and the latter can consequently keep up its speed. The current induced in the armature windings produces apowerful torque which accelerates the velocity of the vehicle. The counter electromotive force of the motor part thereby begins 'to take efiect. To the same extent the generator excitation can be strengthened again, so that it regains its full value before the actual regulation of the transmission ratio, as described above, commences.

The weakening of the generator field at starting may also be effected automatically, as shown in Fig. 2, by means of the regulating rod 24 in dependence on the centrifugal governor l8 and the resistance 2|. As the speed n: increases, the sleeve ll becomes displaced towards the right, and with it the resistance 2! is also shifted towards the right so that at a certain speed m the resistance 2! is completely cut oil." The size of this resistance can easily be computed.

As already mentioned, the direction of rota- .tion of the shaft 2 is opposed to the direction gearing acting as a motor is excited powerfully but with reversed polarity. For this purpose there is interposed for example a pole reverser 28 in the lead 33 to the exciting winding of the part acting as a motor.

With the aid of the described device it is also possible to start up the driving engine. Fig. 4 shows the arrangement of connections forv the normal workingof the gearing according to the present invention. Mm and Ma denote the torques exerted upon the communal yoke, while Ma is the torque of the driving shaft and Mm the .torque taken up by the fixed casing. In this case the torques'exerted on the mechanically coupled field windings connected to the driven shaft are additive.

Fig. 5 shows an arrangement of connections with the aid of which the drivin engine can be started up by the gearing operated from a battery, without the exertion of torque upon the Cardan shaft. The direction of the exciting current, and the magnitude of the resistances an and w, are such that the torques Mm and Ma exerted upon the common yoke counteract each other and are of the same magnitude. The torque Mm is taken up by the stationary casing. There thus remains the equally powerful but opposite torque My which turns over and starts up the driving engine.

The gearing according to.the present invention also acts as transmission gearing, as already described, when energy is to be transmitted in the opposite direction, from the shaft 2 to the shaft I. This is the case when the driving engine is to be used as a motor brake. In'this case the motor part assumes the function of the generator and the generator part the function of the motor. The latter compels the setting up of a speed 111 which is higher than the speed m, so that the internal combustion engine takes over and destroys the braking energy. The transmispedal i 9 is adapted to actuate both the system of regulating rods 20, 22, 2| for the brushing contacts 24 and also the control rod 22 for the carburetor. The pedal 21 on the other hand operates only the system of rods 20, 22, 2| for the brushing contacts 24 and not the rod 28 for the carburetor. The pedal 21 thus serves for braking, while the pedal II represents the accelerator or gas pedal in the hitherto usual sense of the term.

The above described automatic control of the transmission ratio is not only applicable to electric transmissions. It can also be appropriately applied to all transmission gearing with gradual variation of the transmission ratio.

I claim:

1. In electric transmission gearing a driving motor, a driving shaft coupled with the said, motor, a driven shaft, two direct current electric machines with separate excitation, the one part of the first of the said machines being coupled to the said driving shaft and the other part of said first machine to thesaid driven shaft, the one part of the second'of the said machines bethe one part of the second of the said machineing coupled to the driven shaft and the other part of said second machinebeing stationary, a field winding on the one of the parts of the said second machine, the armature windings of' both the said machines constituting a.closed currentcircuit, an ohmic resistance anda source of current interposed in the circuit of the field winding of the said second machine, means for varying the said resistance, a regulating device for varying the output of the said driving vinotor, the said regulating device being operatively connected with the said means for varying the resistance so as to make said resistance smaller when the output becomes greater and vice-versa, .and a controlling device-connected with the said driven shaft for controlling the speed of rotation'ofsaid driven shaft, the said controlling device being operatively connected with the said resistance varying means, so as to make the said resistance greater when the speed of rotationincreases and-vice-versa, both the said operations of these means being adapted to influence and cancel each other.

2. In electric transmission gearing a driving motor, a driving shaft coupled with the said motor, a driven shaft, two direct current electric machines with separate-excitation, the one part of the first of the said machines being coupled to the said driving shaft and the other part to the saiddriven shaft, an exciting current circuit comprising a field winding on:the one of the said parts of thesaid first machine,

.being coupled to the driven shaft and the other part of the saidsecondwmachine being stationary, the armature windings of both the said machines constituting a closed current .circuit without the interposition of resistances, and, for

T the generation of a powerful starting torque a current source and an ohmic resistance interposed in the said excitingcurrent circuit of the said first machine, means for altering and cu'tting out this resistance, and a-controlling dethe said gearing, the armature of the second of the said machines being stationary, the field magnet systems of both the said machines being mounted'on a commonyoke and coupled to the said driven shaft, a source of current, switching means for switching the said current source into the current circuit formed by the armature windings of the said two machines, means for adjusting the excitation of 'both the said machines to such a'value that the moments of rotation of the armature of the first and second of the said machines on the commonyoke of the magnet systems just cancel each other out, for the purpose -of starting up the driving motor from. the said source of current.

4. In electric transmission gearing a driving motor, a driving shaftcoupled with the said motor,- a' driven shaft, two direct current electric machines with separate excitation; the one part of the first of the said machines being coupled to the said driving shaft, the other part of the said first machine being coupled to the said driven shaft, the one part of the second of the said machines. being coupled to the driven shaft and the other partof the saidsecond machine being stationary, the armature windings of both thesaid machines constituting a closed current circuit, an exciting current circuit comprising a field winding on the one of the parts of the said second machine, an ohmic resistance and a,

source .of current interposed-in the said exciting current circuit of the said second machine, means vice for varying'the output of the said driving motor, the said regulating device being operatively connected with the said means for varying the resistance so as to make said resistance smaller when the output becomes greater, and vice-versa, a controlling device connected with the said driven shaft for controlling the speed of rotation of the said driven shaft, the said con'- trolling device being operatlvely connected with the said resistance varying means, so as to make the said resistance greater, when the speed of for varying the said resistance, a-regulating de-'- rotation increases and-vice-versa, both the said 45 operations of these means being adapted to infiuence and canceleach other, and a second regulating deviceadapted to alter the said resistance interposed in the said exciting current circuit of the said'secondmachine independent: ly of any alteration in the output of the driving motor, for the purpose of exerting a braking action upon the said driven shaft by powerful excitation of the field of the said second machine.

v I KARL HEFEL, 

